It is known to provide a bore rod or the like with two cutting bits projecting over the forward end of the bore rod and displaced through 180.degree. relative to each other each mounted on a cutting bit carrier which is radially adjustable relative to the bore rod, is guided on a toothing on the bore rod, extends in the direction of adjustment at right angles to the axis of the bore rod, and has parallel teeth, by means of an identical toothing, and which can be fixed relative to the bore rod by means of a clamping screw pausing through an oblong hole in the cutting bit carrier and engaging on the bore rod, there being provided for the radial adjustment of the cutting bit carrier, in each case, an adjusting screw extending in the direction of the toothing and engaging with the cutting bit carrier.
Bore rods of this type provided with two cutting bits displaced through 180.degree. relative to each other, or also tool holders arranged on bore rods so as to be interchangeable, usually serve in this construction for the rough working of bores. Because of the high forces occurring in such processes they must be designed to be very stable. Bore rods with two cutting bits displaced through 180.degree. relative to each other have the basic advantage, compared with tools with one cutting bit, that they can be mounted with double velocity of feed since each cutting bit provides for one removal of swarf. In order to make the edge life of the two cutting bits as near equal as possible the bits must be mounted with equal loading, that is, they must produce the same removal of swarf. For this it is necessary that their effective cut in the axial direction should be arranged to be in a common radial plane and their cutting edges must be at the same distance from the axis of the bore rod. In addition, radial adjustment of the cutting bit carrier is necessary so that different diameters of bore can be worked.
In a known bore rod of the type described in the introduction the bore rod has two recesses displaced through 180.degree. relative to each other at its forward end. The surfaces of these recesses run in a wedge formation towards the forward end of the bore rod. In each of these surfaces there is provided a toothing with parallel teeth which extend at right angles to the axis of the bore rod. Each of the cutting bit carriers is provided with an oblong hole which also extends in the direction of the teeth, and each carrier can be clamped by means of a clamping screw with the interposition of an annular plate. The cutting bit carriers have, in addition,, prolongations projecting beyond the toothing in the axial direction on to which the individual cutting bits are fixed interchangeably, by means of a screw in each case. Fabrication of the two toothings in the recesses on the bore rod entails considerable manufacturing costs. In fact, not only must the recesses be milled out of the cylindricall bore rod but the toothings must also be milled or ground out subsequently. Since the toothings are arranged on different sides of the bore rod care must be taken here that the toothings are not mutually displaced in the axial direction, since in this case the cutting bits would also lie outside a single radial plane. The same is also true for the toothings on the cutting bit carriers. Thus very small tolerances must be observed in manufacture which increases the manufacturing costs. In addition, each cutting bit carrier projects relatively far in the axial direction as measures from its point of attachment by the clamping screw. Added to this, the bore rod is weakened by the recesses. The known tool therefore has low stability which is a disadvantage, particularly in roughing work. In addition in the known bore rods the cutting bit can only be adjusted over a relatively small range.
Bore rods are also known in which the bore rod has a transverse recess at its forward end. Internal toothings, extending at right angles to the axis of the bore rod, are again provided on the surface extending parallel to the axis of the bore rod. In practice these constructions form a kinematic reversal of the previously described bore rods and have the same disadvantages.
In addition bore rods are also known which have a dovetail guide extending along a diameter. The cutting bit carriers are provided with a similar dovetail guide and are fixed by means of a clamping screw extending at right angles to their direction of adjustment. Manufacturing costs for such a dovetail guide are however relatively high without the production of any advantages relative to the bore rod constructiondescribed previously. In particular, however, bore rods with dovetail guides have the disadvantage of large constructional dimensions in particular in the radial direction and a small range of adjustment of the cutting bit carrier relative to the diameter of the bore rod.
One object of the invention is to produce a bore rod or the like of the type described in the introduction with two cutting bit carriers which project over the forward end of the bore rod and which are displaced through 180.degree. relative to each other where said bore rod is simpler in manufacture, more accurate and more stable. In addition an optimal range of adjustment of the cutting bit carriers relative to the diameter of the bore rod should be achieved.
This object is achieved according to the invention in that the toothing for the two cutting bit carriers on the forward surface of the bore rod or the like is provided, in its longitudinal direction, with continuous teeth in a common radial plane over the whole breadth of the forward surface and the cutting bit carriers have a similar toothing on the rear ends which are turned towards the forward face of the bore rod and that the clamping screws are arranged parallel to the axis of the bore rod.
the novel bore rods or the like and their cutting bit carriers are particularly simple to manufacture. Since the toothing for both cutting bit carriers is provided on the forward face no errors can arise in the axial direction. The toothing can be easily fabricated in particular when it, preferably, extends over the whole forward face of the bore rod or the like. The toothing for both cutting bit carriers can be produced in one working operation. The novel tool is thus simpler to manufacture and also more accurate. In addition, the bore rod or the like is not weakened by any recesses and the clamping screws engage in the immediate neighbourhood of the cutting bits so that an optimal stability is produced. In addition as great as possible a range of adjustment of the cutting bit carriers is also produced since the toothing extends over the whole diameter of the bore rod or the like and a maximal bearing area is thereby produced between the cutting bit carriers and the bore rod or the like.